Study of Frustration Effects in Two-Dimensional Triangular Lattice Antiferromagnets—Neutron Powder Diffraction Study of VX₂, X≡Cl, Br and I

Abstract

In order to study the frustration effects, we have taken powder diffraction patterns of VX₂, X≡Cl, Br and I) which are thought to be quasi-two-dimensional triangular lattice antiferromagnets. The spins in VCl₂, VBr₂ and VI₂ were found to order at 36.0, 29.5 and 16.3 K respectively forming a three sublattice structure in the basal plane. Contrary to our expectation, a partially ordered model gives a better fit to the observed diffraction rather than the Néel state with 120° structure though the spins are of Heisenberg symmetry. In VCl₂ and VBr₂, strong diffuse scattering can be observed not only at T>T_N but also at T<<T_N. No critical scattering characteristic for 2D could be seen but the temperature variation of sublattice magnetization is rather close to that for the Ising system.